Possibility engine

The possibility engine was a cybernetic machine built by Rassilon on Gallifrey during the Last Great Time War. It could be consulted about decisions to make in the conflict, since it was able to see the past and the future in the time vortex. It needed a Time Lord whose timeline was retro-evolved. One of the effects of this was a Time Lord to be in constant flux, changing between each of their past and future incarnations.